In just one concise and lucidly written volume a multitude of topics is covered introducing the results of extensive research on the processing of environmental information in vertebrates. Practical examples are provided to illustrate points made in the text. Many factors, both from the external environment and from within the animals own cells or tissue makeup can directly serve as a pressure to elicit physiological and/or behavioral responses in the organisms studied. Light intensity, photoperiod, circadian rhythms, seasonal variation and daylenght, just to name a few, are among the environmental factors that are correlated in these studies to behavioral or hormonal changes, organ function, and reproduction. This work will serve as a guidebook and easy reference source for students and research professionals in physiology, endocrinology, comparative zoology, and veterinary science.